1. Technical Field
This invention relates generally to telephone systems and in particular to signal detectors with echo cancellation features.
2. Related Art
Advances in technology have increased the features available to telephone service subscribers. One widely offered and commonly subscribed to advanced feature is caller identification and call waiting. Caller identifier (xe2x80x9ccaller IDxe2x80x9d) allows a subscriber to received information at the time of a call regarding the calling number and, in some instances, the name of the calling party. This information appears on a display or screen. Call waiting allows a subscriber to receive an indication, often an audible series of beeps while the subscriber is using the telephone, that another party is calling their number. Caller ID and call waiting can be combined so that while a subscriber is on the telephone, the call waiting feature will notify the subscriber of an incoming call and the caller ID display will provide information about the calling party.
The caller ID and call waiting information is sent to the subscriber, and in particular, to the customer premise equipment (xe2x80x9cCPExe2x80x9d) using special tones known as customer premise alert signals (xe2x80x9cCASxe2x80x9d). These signals are sent over standard telephone lines. The CPE includes a monitor or detector, often referred to as CAS detector that monitors for CAS.
There are numerous other types of systems that rely on receipt of detected alert signals for operation. CAS detectors that detect caller ID and call waiting information are one exemplary system that relies on monitoring and detection of transmitted alert signals for desired operation.
Regardless of the particular type of system that relies on the detection of signals for proper operation, one important aspect of operation is that these types of systems accurately detect when a signal is being sent and thereafter accurately receive the signal. Failure to accurately detect or receive a signal prevents the system from operating. In the case of caller ID and call waiting signals, failure to detect a CAS signal will lead to missed calls or failure of the call waiting display to provide the desired information regarding an incoming call.
One problem with prior art CAS detectors is that the signal detectors have difficulty detecting the alert signals. This is especially true for CAS sent while the telephone is off-hook and conversation is occurring. The conversation on the line often disrupts desired detector operation and may lead to missed detects or false detects. A false detect is when the detector falsely detects a signal and initiates action based on the false detect.
Another deficiency is that the operational environment often creates additional unwanted signals and noise that can further disrupt operation of the signal detectors. One example of an undesirable signal that may disrupt desired detector operation is echo. One source of unwanted echo is from a hybrid, a device commonly found in telephones to convert the incoming/outgoing signal path from two conductors to four conductors. Conversely, a hybrid also reduces the signal path from four conductors carrying signals from the telephone to two conductors for transmission to the central office. As signals pass through the hybrid, which is typically not perfectly isolated, reflection signals are created. In addition, the hybrid may create side tones that further disrupt desired detector operation. As a result there is a need for an alert detector configured to reduce or eliminate missed detects or false detects.
The invention provides a system to overcome the undesired effects of the echo that is generated as a signal passes through apparatus of a telephone network. This invention also provides a system for alert detection. Alert detection comprises the monitoring of a received signal for an alert signal. The received signal may comprise a plurality of various signals that interfere with the accurate detection of the alert signal. In an alternative embodiment, signals other than an alert signal may be detected by the invention.
In one embodiment, the invention comprises a signal processor configured to tap into an input line and into an output line, the input line carrying a received signal, the output line carrying a transmitted signal. The signal processor processes the received and transmitted signals to remove various unwanted portions from the received signal to facilitate more accurate detection of the alert or other signals. Removing the unwanted portions of the received signal improves detector operation by reducing signals that may trigger false detects or missed detects. In one embodiment the unwanted signal portions comprise near end echo.
The detector may be configured to receive the processed signal and detect an alert. In alternative embodiments, the invention may comprise a receiver connected to the input line and the detector such that the detector selectively activates the receive when the detector detects an alert signal. Thus the detector activates the receiver to receive data or other information upon detection of an alert signal. In one embodiment, the receiver may be configured to receive and demodulate frequency shift key modulated signals.
In one example operational mode, the invention may improve the accuracy of a signal detector configured to detect a first signal on an input carrying a combined signal. The combined signal may intermittently comprise multiple signals, such as a first, second and third signal. In example method, the system receives and filters the combined signal to remove or reduce the third signal. Next, the invention monitors the filtered combined signal to detected when the first signal is part of the combined signal. In this manner the accuracy of monitoring is improved by removing the third signal because the third signal may comprise an echo signal. The first signal may comprise a customer premise alert signal (xe2x80x9cCASxe2x80x9d). The second signal may comprise a voice signal.
In one embodiment the method also comprises activating a detector to receive a forth signal, the fourth signal being sent from a remote location after the monitoring detects the first signal. The fourth signal may comprise caller ID information.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.